This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Reagent enzymes are the unsung heroes in the field of life sciences research. From restriction enzymes, ligases, to polymerases and exonucleaes, these enzymes play critical roles in all types of nucleic acid analysis. Here we propose to use SSRL x-ray source to obtain high-resolution crystal structures of various reagent enzymes including DNA polymerase, exonuclease, reverse transcriptase, and their complexes with DNA and proprietary nucleotides. The structural information obtained will be utilized to design novel active site chemistries of these enzymes as better tools for life sciences research.